At this time I don't have any copper clad board. I'm waiting for 6 experimenter boards to arrive. I also don't have any coil wire.
I can get these locally I guess so next week I'll go buy them.
For now, sim is fun because osc. are new for me to "design".
The colpitts will be easier to simulate.
A few pages back in this thread is SV's example of using tuna cans to make a "tunable" oscillator.At this time I don't have any copper clad board.
A few pages back in this thread is SV's example of using tuna cans to make a "tunable" oscillator.
I think the sardine cans, being sort of squarish, look better myself.
It is a Hartley oscillator and the advantage over Nigel's suggested Colpitts is the Colpitts is split stater capacitors which means they will appear in parallel and therefore will not have the same capacitance range as a single tuning cap.
Dump the simulator, get the soldering iron and some real components, connect them up on a breadboard* and try it for real.
WHAT??
Where did split stator capacitor come from?
You dont need a split stator capacitor in a colpits oscillator.
Have a look here: colpitts oscillators
JimB
OK man. You see the two capacitors C1 & C2? Well, if you are interesting in making the Colpitts into a VFO, then they will be variable and if you make only one variable it will not change the frequency nearly as much as making them both variable. Hence...split stator or ganged capacitors.
Also it is much cheaper to build a coil with a tap, than it is to buy a split stator capacitor.
C1 and C2 aren't the tuning capacitors, they are the feedback capacitors, that rather useless partial diagram doesn't show the tuning capacitor which is directly across the coil and is only a single gang one.
Without referencing anything, I am sure I have seen C1 & C2 as ganged variable caps. These would be used for your main tuning or broad tuning range. There most certainly are other ways to tune the Colpitts, but they will not be as broad.
Any differences would be slight, and certainly using ganged feedback capacitors to tune a colpitts would be extremely unusual (I don't think I've ever seen it, or even seen it suggested before?) - how broard a tuning range are you looking for? - aren't we talking amateur bands here?.
As far as a tapped coil as opposed to an inefficient single variable cap in a Colpitts. I can make a tapped coil for less than a penny. That includes the solder....chop chop!
But, as everyone has said, single variable tuning on a colpitts isn't inefficient, it's perfectly efficient and works exceedingly well. An added advantage of the colpitts is that band switching is easier, only one pole to switch rather than two.
Nothing wrong with a Hartley, but you appear to be dismissing Colpitts for only imaginary reasons.
The ratio of the two caps is not critical. You want the stage gain to be a little over one to sustain oscillation only. In practical circuits one variable cap will be enough, not counting a trimmer.
Then there is the series tuned colpitts. In this circuit the feedback caps are only used for feedback.
Is this not correct?
and thank you SV for the additional info on your circuit.
I would like to know a ballpark figure for the total reactance of the inductor. It makes choosing one easier for any frequency desired.
Here's a good website basically describing what I'm talking about with the ganged series capacitors:
**broken link removed**
Don't know about it been a 'good' website, but that circuit is the wierdest looking colpitts I've ever seen - googling round it looks to be based on the original valve colpitts design.
Colpitts oscillators are usually built using a common collector circuit, or for VHF/UHF using common base (like all the many FM bug circuits).
It's the AC feedback path that determines the type of oscillator. Doesn't have anything to do with transistor or tube configuration.
No, but certain configurations are used for certain reasons - and the diagram you posted the link to was a particularly strange one, that makes life difficult
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